| 1. |
- Agosta, Lorenzo, et al.
(författare)
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Adsorption of Glycine on TiO2 in Water from On-the-fly Free-Energy Calculations and In Situ Electrochemical Impedance Spectroscopy
- 2024
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Ingår i: Langmuir. - 0743-7463 .- 1520-5827. ; 40:23, s. 12009-12016
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Tidskriftsartikel (refereegranskat)abstract
- We report here an experimental-computational study of hydrated TiO2 anatase nanoparticles interacting with glycine, where we obtain quantitative agreement of the measured adsorption free energies. Ab initio simulations are performed within the tight binding and density functional theory in combination with enhanced free-energy sampling techniques, which exploit the thermodynamic integration of the unbiased mean forces collected on-the-fly along the molecular dynamics trajectories. The experiments adopt a new and efficient setup for electrochemical impedance spectroscopy measurements based on portable screen-printed gold electrodes, which allows fast and in situ signal assessment. The measured adsorption free energy is −30 kJ/mol (both from experiment and calculation), with preferential interaction of the charged group which strongly adsorbs on the TiO2 bridging oxygens. This highlights the importance of the terminal amino groups in the adsorption mechanism of amino acids on hydrated metal oxides. The excellent agreement between computation and experiment for this amino acid opens the doors to the exploration of the interaction free energies for other moderately complex bionano systems.
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| 2. |
- Agosta, Lorenzo, 1986-
(författare)
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Atomistic simulations of structural and dynamical properties of liquids under geometric constraints
- 2019
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- The statistical-mechanical description of liquids represents a formidable problem in physic due to the absence of the analytical theory of the liquid state. Atomistic simulations represent a unique source of information in this respect and can be implemented in order address macroscopically measurable liquid properties, including its structure and dynamics, based on the information of the interactions between its constituent molecules. A particularly intriguing challenge is represented by the problem of studying liquids under geometric constraints like surfaces, or where the dimensionality is strongly suppressed like for liquids in 2 dimensions. Experimental measurements cannot access to these regions due to the resolution limitations. In this thesis the study of confined liquids is achieved by particle-based simulations at different level of theory. In particular 3 study cases are considered: the first is the characterization of solid-liquid interfaces. The problem of adsorbing surfaces is treated as a specific case of inorganic surfaces in contact with liquid water. TiO2, chosen as reference material, is studied in its polymorphic structures in aqueous conditions. The surface reactivity and its influence on the liquid structure is solved considering the quantum nature of the system. The mechanism of a solute adsorbing at the interface, considering the interfacial liquid properties, is also addressed. New advanced analysis tools for determining the structural and dynamical properties of water under a surface confinement and the thermodynamic associated to relative adsorption processes are developed. We are confident that this study will represent a mile stone for a systematic study of complex environments as bio-inorganic interfaces. As second case a liquid confined in a 2D surface is studied. Simple liquids having spherically symmetric interaction are very powerful in order to understand the relevant degrees of freedom that governs a certain physical process. Here we expand the definition of 2D hexatic phases to smectic systems in 3D. Finally the self-assembly of a triply periodic mesophase having a Fddd space symmetry group is fully characterized for a simple liquid. This phase can be thought as a geometrical reduction to a two-dimensional separation surface. The possibility of generating such complex network with simple particles, like in colloids, opens the frontiers for the exploration of new materials and applications.
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| 3. |
- Agosta, Lorenzo, et al.
(författare)
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Diffusion and reaction pathways of water near fully hydrated TiO2 surfaces from ab initio molecular dynamics
- 2017
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Ingår i: Journal of Chemical Physics. - : AIP Publishing. - 0021-9606 .- 1089-7690. ; 147:2
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Tidskriftsartikel (refereegranskat)abstract
- Ab initio molecular dynamics simulations are reported forwater-embedded TiO2 surfaces to determine the diffusive and reactive behavior at full hydration. A three-domain model is developed for six surfaces [rutile (110), (100), and (001), and anatase (101), (100), and (001)] which describes waters as hard (irreversibly bound to the surface), soft (with reduced mobility but orientation freedom near the surface), or bulk. The model explains previous experimental data and provides a detailed picture of water diffusion near TiO2 surfaces. Water reactivity is analyzed with a graph-theoretic approach that reveals a number of reaction pathways on TiO2 which occur at full hydration, in addition to direct water splitting. Hydronium (H3O+) is identified to be a key intermediate state, which facilitates water dissociation by proton hopping between intact and dissociated waters near the surfaces. These discoveries significantly improve the understanding of nanoscale water dynamics and reactivity at TiO2 interfaces under ambient conditions.
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| 4. |
- Agosta, Lorenzo, et al.
(författare)
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Hexatic smectic phase with algebraically decaying bond-orientational order
- 2018
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Ingår i: Physical review. E. - : American Physical Society. - 2470-0045 .- 2470-0053. ; 97:5
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Tidskriftsartikel (refereegranskat)abstract
- The hexatic phase predicted by the theories of two-dimensional melting is characterized by the power-law decay of the orientational correlations, whereas the in-layer bond orientational order in all the hexatic smectic phases observed so far was found to be long range. We report a hexatic smectic phase where the in-layer bond orientational correlations decay algebraically, in quantitative agreement with the hexatic ordering predicted by the theory for two dimensions. The phase was formed in a molecular dynamics simulation of a one-component system of particles interacting via a spherically symmetric potential. The present results thus demonstrate that the theoretically predicted two-dimensional hexatic order can exist in a three-dimensional system.
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| 5. |
- Agosta, Lorenzo, et al.
(författare)
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Improved Sampling in Ab Initio-Based Free Energy Calculations of Amino Acids at Solid-Liquid Interfaces : A Tight-Binding Assessment on TiO2 Anatase (101)
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Annan publikation (övrigt vetenskapligt/konstnärligt)abstract
- Atomistic simulations are powerful for probing molecules at bioinorganic interfaces and excellent complements to scarcely available experimental techniques. The free energy controls the adsorption behavior of molecules on nanosurfaces, and is therefore a quantity of particular importance. Advanced sampling techniques can efficiently explore the adsorption free energy landscape, but molecular simulations with classical (Newtownian) dynamics fail to capture charge transfer and polarization at the solid-liquid interface. First principle simulations do not suffer from this limitation but come with a heavy computational load. Here, we introduce an efficient protocol to explore the free energy of adsorption in the ab initio framework. This approach accurately models the complex phenomena at bio-inorganic surfaces on the nanoscale and properly samples the relevant thermodynamic properties. We present a case study of adsorption of the Lysine and Aspartate amino acids on the anatase (101) TiO2 surface with the tight binding method. The high values of the calculated adsorption free energies highlight the importance of a proper description of the electronic state for surface binding processes.
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| 6. |
- Agosta, Lorenzo, et al.
(författare)
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Improved Sampling in Ab Initio Free Energy Calculations of Biomolecules at Solid-Liquid Interfaces : Tight-Binding Assessment of Charged Amino Acids on TiO2 Anatase (101)
- 2020
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Ingår i: Computation. - : MDPI AG. - 2079-3197. ; 8:1
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Tidskriftsartikel (refereegranskat)abstract
- Atomistic simulations can complement the scarce experimental data on free energies of molecules at bio-inorganic interfaces. In molecular simulations, adsorption free energy landscapes are efficiently explored with advanced sampling methods, but classical dynamics is unable to capture charge transfer and polarization at the solid-liquid interface. Ab initio simulations do not suffer from this flaw, but only at the expense of an overwhelming computational cost. Here, we introduce a protocol for adsorption free energy calculations that improves sampling on the timescales relevant to ab initio simulations. As a case study, we calculate adsorption free energies of the charged amino acids Lysine and Aspartate on the fully hydrated anatase (101) TiO2 surface using tight-binding forces. We find that the first-principle description of the system significantly contributes to the adsorption free energies, which is overlooked by calculations with previous methods.
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| 7. |
- Agosta, Lorenzo, et al.
(författare)
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Origin of the Hydrophobic Behaviour of Hydrophilic CeO2
- 2023
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Ingår i: Angewandte Chemie International Edition. - : Wiley-VCH Verlagsgesellschaft. - 1433-7851 .- 1521-3773. ; 62:35
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Tidskriftsartikel (refereegranskat)abstract
- The nature of the hydrophobicity found in rare-earth oxides is intriguing. The CeO2 (100) surface, despite its strongly hydrophilic nature, exhibits hydrophobic behaviour when immersed in water. In order to understand this puzzling and counter-intuitive effect we performed a detailed analysis of the water structure and dynamics. We report here an ab-initio molecular dynamics simulation (AIMD) study which demonstrates that the first water layer, in immediate contact with the hydroxylated CeO2 surface, is responsible for the effect behaving as a hydrophobic interface with respect to the rest of the liquid water. The hydrophobicity is manifested in several ways: a considerable diffusion enhancement of the confined liquid water as compared with bulk water at the same thermodynamic condition, a weak adhesion energy and few H-bonds above the hydrophobic water layer, which may also sustain a water droplet. These findings introduce a new concept in water/rare-earth oxide interfaces: hydrophobicity mediated by specific water patterns on a hydrophilic surface.
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| 8. |
- Agosta, Lorenzo, et al.
(författare)
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Self-assembly of a triply periodic continuous mesophase with Fddd symmetry in simple one-component liquids
- 2020
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Ingår i: Journal of Chemical Physics. - : AIP Publishing. - 0021-9606 .- 1089-7690. ; 152:19
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Tidskriftsartikel (refereegranskat)abstract
- Triply periodic continuous morphologies (networks) arising as a result of the microphase separation in block copolymer melts have so far never been observed self-assembled in systems of particles with spherically symmetric interaction. We report a molecular dynamics simulation where two simple one-component liquids form upon cooling an equilibrium network with the Fddd space group symmetry. This complexity reduction in the liquid network formation in terms of the particle geometry and the number of components evidences the generic nature of this class of phase transition, suggesting opportunities for producing these structures in a variety of new systems.
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| 9. |
- Agosta, Lorenzo, et al.
(författare)
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Self-assembly of orthorhombic Fddd network in simple one-component liquids
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Annan publikation (övrigt vetenskapligt/konstnärligt)abstract
- Triply periodic continuous morphologies arising a result of the microphase separation in block copolymer melts have so far never been observed self-assembled in systems of particles with spherically symmetric interaction. We report a molecular dynamics simulation of two simple one-component liquids which self-assemble upon cooling into equilibrium orthorhombic continuous network morphologies with the Fddd space group symmetry reproducing the structure of those observed in block copolymers. The finding that the geometry of constituent molecules isn't relevant for the formation of triply periodic networks indicates the generic nature of this class of phase transition.
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| 10. |
- Agosta, Lorenzo, et al.
(författare)
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Supercooled liquid-like dynamics in water near a fully hydrated titania surface : Decoupling of rotational and translational diffusion
- 2021
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Ingår i: Journal of Chemical Physics. - : American Institute of Physics (AIP). - 0021-9606 .- 1089-7690. ; 154:9
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Tidskriftsartikel (refereegranskat)abstract
- We report an ab initio molecular dynamics (MD) simulation investigating the effect of a fully hydrated surface of TiO2 on the water dynamics. It is found that the universal relation between the rotational and translational diffusion characteristics of bulk water is broken in the water layers near the surface with the rotational diffusion demonstrating progressive retardation relative to the translational diffusion when approaching the surface. This kind of rotation-translation decoupling has so far only been observed in the supercooled liquids approaching glass transition, and its observation in water at a normal liquid temperature is of conceptual interest. This finding is also of interest for the application-significant studies of the water interaction with fully hydrated nanoparticles. We note that this is the first observation of rotation-translation decoupling in an ab initio MD simulation of water.
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